import inspect

class Registry(object):

    def __init__(self, name):
        self._name = name
        self._module_dict = dict()

    def __repr__(self):
        format_str = self.__class__.__name__ + '(name={}, items={})'.format(
            self._name, list(self._module_dict.keys()))
        return format_str

    @property
    def name(self):
        return self._name

    @property
    def module_dict(self):
        return self._module_dict

    def __getattr__(self, key):
        if not key in self._module_dict:
            raise KeyError("not found register module `{}` in Register('{}')".format(
                key, self._name))
        return self._module_dict.get(key, None)
    

    def _register_module(self, module_class):
        """Register a module.
        Args:
            module (:obj:`nn.Module`): Module to be registered.
        """
        if not (inspect.isclass(module_class) or inspect.isfunction(module_class)):
            raise TypeError('module must be a class or a function, but got {}'.format(
                type(module_class)))
        module_name = module_class.__name__
        if module_name in self._module_dict:
            raise KeyError('{} is already registered in {}'.format(
                module_name, self.name))
        self._module_dict[module_name] = module_class

    def register(self, cls):
        self._register_module(cls)
        return cls

DATA_LOADERS = Registry('data_loaders')
MODELS = Registry('model')
LOSSES = Registry('loss')
METRICS = Registry('metric')